[Amps] HF amp output power dropping

[Tom Rauch]

Sorry about that, I posted last week and and didn't know how 
to do a follow up on the thread.
The amp is a homebrew 3CX3000a7. I did not build it myself.
Plate current and plate voltage behave as always under load.
Output power drops with steady drive applied. 400 watts will 
drop to 350.
Aside from the output power falling off, the filament 
voltage (which always used to drop a little when I would key 
up) has begun to rise when I key up.
The more drive I give it, the higher the filament voltage 
rises.  Used to always drop under load.
>>>

Are you saying when the power output drops the plate current 
doesn't change?

What about the grid current?

What ALL the meters do, including grid current and exciter 
SWR, will tell you a great deal. Without knowing what the 
meters do all people can do is guess, and that isn't very 
productive.

73 Tom